This invention relates to vinyl halide homopolymers and copolymers intended to be dissolved in solvents and used to produce fibers, to cast films and for coatings for various substrates.
Vinyl halide homopolymers and copolymers, especially polymers of vinyl chloride, are typically produced by suspension polymerization of the monomers in the presence of a suspending agent. It is found that when such polymers are dissolved in solvents and used as casting solutions or as coatings for substrates, undesirable "specs" or "seeds" are found in the coating and casting solutions. Moreover, the films resulting from casting or from coating the solutions on substrates are hazy in appearance and/or have a "grainy" appearance when the solvent evaporates. Fibers produced from such solutions tend to break at the points where specs or seeds occur. These adverse effects are believed to be caused by the fact that the suspending agent is insoluble in the common solvents. The insoluble particles produce the undesirable effects just described.
U.S. Pat. No. 4,355,146 describes a process for producing a vinyl chloride resin which comprises subjecting a vinyl chloride monomer and co-monomers to suspension polymerization in an aqueous medium using a water-soluble protein as a suspending agent, and treating the resulting polymer with a proteolytic enzyme. The resulting polyvinyl chloride (PVC) is referred to as "blending PVC" and is said to be compounded with a "paste PVC" to give a paste dispersion having excellent viscosity properties for which molded articles having superior tensile strength, abrasion resistance, weatherability, water resistance, etc., can be produced. The patentees state that the water-soluble protein used as the suspending agent and remaining on the surface of the polymer particles can be decomposed by very simple and low cost method which comprises treating the resulting polymer with a proteolytic enzyme, or protease. The patentees further disclose that proteins can be hydrolyzed with acids or alkalies, but this requires a long period of time or severe conditions with regard to temperature, concentration, etc. The patentees state that the use of such a hydrolyzing method in the decomposition of the remaining protein on the polymer surface reduces productivity or degrades the properties of the resulting product.
German Offenlegungsschrift No. 2,206,903 (Aug. 23, 1973) discloses preparation of polyvinyl chloride by aqueous phase suspension polymerization in the presence of cellulose ethers. Post treatment with cellulase in an aqueous suspension at a pH value of between 7 and 3 is disclosed. The treatment is disclosed to improve the absorption of plasticizers and the gelling of the PVC. The improved gelling is said to improve the break resistance at low temperatures of molded articles. Example 1 of the patent shows that when a thin film is milled from PVC that was treated with cellulase, the film has better low temperature strength than a film made of untreated PVC. The product contemplated in the patent is not a solution grade product, and hence not relevant to the present invention.
Japanese Patent Publication Sho No. 58-91716 (May 31, 1983), discloses preparing graft polymers of thermoplastic particles and vinyl monomers such as styrene in a suspension polymerization process. The polymer product was washed with acid; and the suspending agent was removed.
A data sheet pertaining to Methocel cellulose ether products discloses that Methocel cellulose ether products in strong acids or in strong caustic solutions will decrease in viscosity. Such loss in viscosity is indicative that hydrolysis is occurring. Nevertheless, from this disclosure, the results of the present invention cannot be foreseen.
The object of this invention is to treat vinyl halide resin particles in an effective and efficient manner with an acidic solution to remove and/or solubilize the suspending agent such that the resulting resins can be used to produce clear polymer solutions that are suitable for producing fibers, casting films and for the coating of substrates.